25 Jul 2022

Resin-Rich HV Coils For Class H Applications

UK-based Preformed Windings, has launched QualCoil H, the first resin-rich diamond coil specification suitable for class H motors and generators.

The cutting-edge QualCoil H specification has been developed in-house within the Preformed Windings lab, and in collaboration with a leading insulation manufacturer, large OEM and industry thought leaders.

Commenting on the launch, James Stevens, Global Sales and Marketing Director, said: “We are very excited to announce the launch of QualCoil H, the first resin-rich HV coils specification suitable for class H applications. This specification offers all the benefits of resin-rich technology and is proving hugely popular in industries such as hydro, nuclear and critical industrial applications where reduced maintenance and longevity are key. Preformed Windings is very proud to be thought leaders in HV diamond coil design and manufacturing with a position as independent product manufacturers allowing us to collaborate with the most respected individuals and organisations in the industry”.

QualCoil H has successfully passed 2,000 hours of voltage endurance testing, where a pass criteria is typically 250 hours or 400 hours. The lab testing the coils had to ask permission to turn the test off as there were sets of coils queued behind the QualCoil H coils that required testing. The test coils were in exceptional condition despite the 2,000 hours of extreme testing and passed all typical type testing along with giving exceptional partial discharge and tan delta results.

Preformed Windings and its partners want to explore the capabilities of QualCoil H, and the specification is currently undergoing stringent through-life testing to include cyclic thermal cycle, voltage endurance, vibration and extreme temperature testing at a leading European test facility along with other QualCoil specifications.

While QualCoil H is suitable for Class H applications, it offers significant benefits to machines at lower temperature classes. The delta between a machine’s actual operating temperature and the maximum allowable operating temperature of the insulation is typically a good indicator of the life of the coils insulation system. If this delta is larger, the insulation system will last longer, and therefore QualCoil H is offering longer service life to Class F motors and generators. This benefit is being experienced in the industry with GE Renewables saying: “Preformed Windings has supplied many sets of high voltage coils to GE Renewables over the years. The quality of product and service is exceptional, and it is a trusted partner in our supply chain. We enjoy collaborative and cutting-edge research and development with Preformed Windings, which positions both organisations as thought leaders in the hydro industry. Its products offer significant benefits such as very low partial discharge and long service life".


Preformed Windings is passionate about sustainability, and QualCoil H was initially designed as a coil specification for the hydro repair market. The International Energy Agency (IEA) says there is a need to double hydropower capacity by 2050 to meet the Paris climate targets. However, the development of new hydro facilities is slow and expensive. Many of the hydro facilities in North America and Europe are approaching the service life of their generators, and there is a huge opportunity not only to repair existing assets but improve them to offer longer service life and increased output.

Through the careful redesign of the HV diamond coils and the utilisation of cutting-edge specifications such as QualCoil H, Preformed Windings can offer the industry a viable solution to utilise existing assets while increasing renewable energy outputs.

Another industry expert, Sidewinders LLC, said: “Preformed Windings’ engineers listen to each client’s needs and study the specific requirements of each project to provide precisely tailored solutions. Preformed Windings uses its position as a trusted thought leader in the industry not simply to manufacture replacement coils, but to improve coil designs substantially. Preformed Windings’ process and focus on continuous improvement results in superior machine performance that will endure for many years to come.”

As a member of the Association of Electrical and Mechanical Trades (AEMT), the Electrical Apparatus Service Association (EASA), and the National Hydropower Association (NHA), Preformed Windings is looking to collaborate further on developing this key product for the service industry and is inviting industry experts to open a dialogue and collaboration industry-wide to contribute to the circular economy and sustainability goals.